1. Field of the Invention
This invention is directed to a solid-state lighting device, such as light emitting diode (LED) device, for illumination as a primary light source as well as for emergency or security situations.
2. Discussion of Related Art
The National Electric Code (NEC) mandates that commercial buildings provide emergency egress lighting in case of power failures. As such, various primary and secondary light source systems have been developed for the entryways of public buildings. In general, these systems have a primary light source which is powered off the electrical grid and provides ample luminance for normal operation. A secondary emergency light source can provide at least a minimum luminance for an extended duration, as established by the NEC standard, until the primary light source is working.
In these dual purpose egress lighting systems, the primary light source needs to provide specified lighting parameters, while the secondary light source needs to provide a minimum level of lighting for an extended duration. Known dual purpose systems use an incandescent or other type of bulb, which provides ample lighting, in combination with an LED, which can provide a minimum level of light for extended periods while drawing minimum amount of power. Such a system is disclosed in U.S. Pat. No. 6,909,239, the entire teachings of which are incorporated into and made a part of this specification by reference to U.S. Pat. No. 6,909,239. However, the incandescent bulbs of such systems are inefficient because they draw significant power and require maintenance to replace the incandescent bulb when it burns out.
There is a continuing need for an improved lighting system which utilizes an efficient light source, such as LEDs, with the dual purpose of providing both a primary lighting source as well as an emergency lighting source and for such a system to comply with NEC standards for emergency egress lighting.